Since the establishment of the Center for the Care and Treatment of Sexually Dangerous Persons at Bridgewater in 1959, some 1300 cases have been referred to it for evaluation. These assessments, which each required a minimum of 60 days, involved clinical examinations, psychological tests, the meticulous reconstruction of the patient's life histories from multiple sources (the patient himself, his family, teachers, and employers), and the scrutiny of court, correctional, and mental hospital records. The reports from these evaluations, along with copies of substantial parts of the raw data from which these reports were generated, are now on file at Bridgewater. These clinical files can serve as a rich data base to address a number of important questions about the subtyping of sexually dangerous persons. Using these files, we propose to code all patients on a large number of variables (nature and frequency of their crimes, predisposing and precipitating factors, demographic characteristics, family patterns, etc.), to rate them all on several scales and on diagnostic criteria, to attempt to apply a clinically-derived subtyping scheme, and to generate empirical subtypes. The transformation of these files into quantified dimensions and specific categories will allow a systematic investigation of whether homogeneous subtypes exist within this sample. The concurrent validity of these subtyping schemes will be assessed by examining type differences on standardized interviews and testing of the present resident population. The quantification of this rich data source, and the generation and validation of cohesive subtypes will contribute substantially to our knowledge of these aggressive and/or repetitive sexual offenders, and will lay a firm empirical foundation for subsequent studies.